Process of injection molding composite articles and toothbrush obtainable thereby

ABSTRACT

An injection moulding process for making a moulded article particularly a toothbrush consisting partly of a hard first plastics material by providing a first injection mould introducing a component into the cavity adjacent to the surface; injecting a plastics material into the cavity so that the plastic material is fixed to the component and the component forms part of the outer surface of the article. In a second moulding operation another material such as an elastomer may be injected. A toothbrush product made by this process is also described.

[0001] This invention relates to a process for making moulded articles,particularly toothbrushes, and to a product moulded article made usingthis process, particularly a toothbrush.

[0002] Toothbrushes are well known articles and are generally made ofhard plastics materials such as polypropylene, polyamide or styro acrylnitrol (“SAN”), almost invariably by means of an injection mouldingprocess. Two component toothbrushes are also known which comprise partsmade of a first material being a hard plastic for example of the typementioned above, and parts made of a second material different to thehard plastic for example an elastomer (rubbery) material. Suitablethermoplastic elastomers suitable for such two component toothbrushesare well known and are now extensively used. See for example EP-A-0 336641 and DE-A-39 23 495 for examples of such toothbrushes. Generally suchtwo-material toothbrushes are made in a two stage injection mouldingprocess in which firstly a “skeleton” comprising the first materialpart(s) is made, and this skeleton is then enclosed in a secondinjection mould into which the second material is injected. Such aprocess is well known, and disclosed for example in WO-A-94/05183.

[0003] It is also known in the brush industry, e.g. from EP-A-0 742 090to embed an insert in a brush handle by positioning the insert in thecavity of an injection mould, first covering one side with a injectedplastic material, and then in a subsequent injection moulding operationcovering the other side with the plastic material. U.S. Pat. No.2,923,035 discloses a method for making plastic articles, particularlybrushes, in which a first piece is first made by injection moulding afirst plastic material in a first mould, a second piece of an opaquematerial is put on top of the first piece, then the assembly of firstand second pieces is positioned in a second mould and encased in asecond mould, and then encased in a second plastic material.

[0004] It is an objection of the present invention to provide a furtherprocess for making toothbrushes, and to provide toothbrushes of enhancedappearance, quality and resistance to wear etc., by the use of a thirdcomponent. Other objects of the invention will become apparent from thefollowing description.

[0005] According to this invention process for making a moulded articleconsisting partly of a hard first plastics material comprises:

[0006] providing a first injection mould having a cavity which definesat least part of the shape of the article and having a cavity surfacebounding the cavity;

[0007] introducing a component into the cavity adjacent to the cavitysurface;

[0008] injecting a first fluid plastics material into the first mouldcavity, under conditions such that the plastics material flows intocontact with the component and when the plastics material solidifies thehardened plastic material is fixed to the component and the componentforms at least part of the outer surface of the article.

[0009] The plastics material may then be allowed to solidifysufficiently that the so formed article can be removed from the mouldcavity.

[0010] The moulded article formed in this process is suitably a part orwhole toothbrush comprising a grip handle part and a head part intowhich bristles may be fixed, either using conventional metal fixingstaples, or by moulding the bristle tufts directly into the head usingany of known “anchorless” processes.

[0011] Suitably the component may comprise a part of the grip handle.The component may for example comprise a decorative and/or a structuralpart. For example the component may be made of a second material in thine.g. sheet form, e.g. 0.01-2.0 mm, preferably 0.1-1.0 mm thick, metalsuch as aluminium or an aluminium alloy, a second plastic (suitably adifferent plastic to the first plastics material) or a metal-plasticlaminate or composite e.g. a metal filled plastic. “Sheet” as usedherein will be understood in the art but for clarity includes primarilyshapes which have a thickness dimension of 0.2 or less, preferably 0.1or less, more preferably 0.05 or less of both their length and widthdimension. If the component comprises a plastic material this shouldhave a softening point higher than that of the first plastics materialor the operating temperature of the injection mould, whichever ishigher, to preserve the structural integrity of the component.

[0012] For example the component may comprise in form a thin shell, asurface of which forms at least part of the outer surface of thefinished article e.g. of a toothbrush, e.g. part of the outer surface ofthe grip handle part of the toothbrush. Such a component may thereforehave a convex outer surface generally conforming to the outer surfaceprofile of the article to be formed, and a concave inner profile beinggenerally a negative of the outer surface profile. For example thecomponent may comprise a thin shell of a decorative foil. The componentmay comprise a decorative component e.g. a shiny or coloured outersurface part, and/or it may help to protect the plastic part of thearticle from wear, and/or it may provide the outer surface of the griphandle with improved grip characteristics such as surface texture.Preferably the component is made robust enough, e.g. being made thickenough, either locally or generally, or may be provided withreinforcements e.g. ribs etc. on its inner surface to resist the forcesof the injection of the first plastic material.

[0013] The injection mould may for example be a multi-part e.g. two partmould where each part defines part of the mould cavity and together theparts define between them the entire mould cavity when the parts closetogether. Multi-part moulds of this type for toothbrush manufacture arewell known.

[0014] Suitably the component is positioned in the mould cavity incontact with the inner surface of the cavity surface so that at leastpart of the component forms part of the outer surface of the article. Itmay be advantageous to include features in the mould, e.g. supports orinternal cores to hold the component in position in the mould cavityduring the first moulding operation.

[0015] Suitable methods of supporting the component in the mould cavitywill be apparent to those skilled in the art.

[0016] The mould and component may have co-operating parts, e.g.respective parts of a multi-part mould may grip the component betweenthem when they close together.

[0017] Preferably the component is held in place in the cavity incontact with the cavity surface, at least immediately prior to andpreferably during the injection of first material, by the application ofreduced atmospheric pressure to the component via a conduit in the mouldand opening at openings into the mould cavity, i.e. sucking thecomponent against the cavity surface. If reduced atmospheric pressure isused in this way preferably the component seals against the mould cavitysurface to maintain the vacuum and to prevent injected first plasticmaterial from leaving the mould cavity via the conduit. Suitabledimensions of conduits and openings and suitable pressures to achievethe above will be apparent to those skilled in the art. It is importantto ensure that the dimensions of any such opening into the mould cavityis not so large that if the component is a thin and relatively fragilefoil then the pressure within the mould cavity when the first plasticmaterial is injected into the mould causes the foil to be punctured atthe opening(s). For example rather than one or a few large opening(s) itmay be preferable to use many small pin-point openings distributed overthe inner surface of the mould cavity where the component comes intocontact with the inner surface. These many openings may communicate witha single vacuum manifold.

[0018] Suitably the component is positioned in the mould cavity byautomatic machinery, such as a robot, for example repeatedly takingcomponents from a storage source or conveyor and inserting themprecisely into the mould cavity for the above-described process to beperformed.

[0019] The first plastics material may be any plastics material known tobe suitable for making the hard plastics parts (e.g. the structure ofthe head, grip handle, neck etc.) of a toothbrush, for example apolypropylene, polyamide or styro lacryl nitrol (¢SAN∞). A typicalsuitable polypropylene is for example Polypropylene Mosten 52945(Marketed by Schulman). Typically such material have a Shore A hardnessof 90-100. Suitable moulding conditions for injecting such plasticmaterials into an injection mould are known from the art.

[0020] Suitable conditions are also known for ensuing that thecomponent, e.g. in the form of the above-described thin sheet, or shell,or metal or comprising a plastics material, fixes securely to the massof hardened first plastics material. For example the inner surfaces ofthe component which come into contact with the first plastic materialmay be provided with barbs or anchor parts which become embedded in thefirst plastics material. Additionally or alternatively adhesion canoccur between the component and the first plastics material, and thesurface(s) of the component which comes into contact with the firstplastic may be appropriately roughened or treated with a bonding aid etcif necessary to enhance adhesion. Additionally or alternatively thecomponent may have cavities in it into which the plastics material canflow to form engagement parts to retain the component in place.Generally adhesion between the first material and surface of thecomponent may be adequate to achieve a bond between the first materialand the component.

[0021] Optionally and preferably the so-formed article, i.e. comprisingthe first material and the component, may be further processed in asecond injection moulding operation by:

[0022] providing a second injection mould part having a second mouldcavity therein;

[0023] introducing the so-formed article into the second mould cavity ofthe second injection mould part;

[0024] injecting a melted fluid third material into the mould and intocontact with the so-formed article;

[0025] allowing the melted fluid third material to solidify sufficientlyand such that when the third material solidifies the hardened thirdmaterial is fixed to the article.

[0026] The so formed article may then be removed from the second mouldcavity.

[0027] The second injection mould may for example again be a multi-parte.g. two part mould where each part defines part of the mould cavity andtogether they form the entire mould cavity. Generally the secondinjection mould will comprise separate parts to the first injectionmould, but one or more parts of the first injection mould may form oneor more parts of the second injection mould.

[0028] The third material may for example be a plastics material whichis suitable for forming hard plastic parts of the article or it maypreferably be for example a rubbery material such as a thermoplasticelastomer. For example such a rubbery material may comprise a grip padof generally known type on the grip handle of an article being atoothbrush. The term “rubbery” as used herein is not limited to rubberitself, either natural or synthetic but includes all materials such aselastomers (also equivalently known as elastomeric materials) havingelastic properties under compression or stretching similar to rubberitself. Suitable rubbery materials are for example thermoplasticelastomers of the type well known in the toothbrush industry for formingtoothbrush grip pads, as for example as sold by the applicant and itsrelated companies under the trade marks “AQUAFRESH” and “Dr BEST”.Suitable rubbery materials include those sold under the trade markSANTOPRENE, and typically have a Shore A hardness from about 10 to 90,preferably 30 to 80 Shore A. Suitable injection moulding conditions forsuch materials to achieve adhesion between the hard plastic materials ofwhich toothbrushes are made are known in the art and have been used inthe manufacture of two-component toothbrushes for several years.

[0029] Suitably one or more hollow in the surface of the article, or oneor more aperture passing through the article may be formed in the firstmoulding operation, which are suitable to receive and to be wholly orpartially filled with, the third material in the second moulding step.Such hollow and aperture may be formed in the stage of injection of theplastic material during the first moulding operation by the provision ofone or more corresponding convex projection from the cavity surface ofthe first injection mould, to thereby leave a hollow or aperturegenerally in the shape of a “negative” of the convex projection. Suchconvex projection, often known in the injection moulding art as aninternal core, may for example extend in a direction across the mouldcavity from one of the parts of the mould toward another.

[0030] The third material may flow into the hollow and/or through theaperture and flow to parts of the article distanced from the injectiongate of the third material. Such hollow or aperture may thereby comprisea moulding channel, generally known in principle, by means of which thethird material may be transmitted from the injection gate to distantparts of the article, such as a toothbrush. By means of such a channelthe third material may be caused to flow into contact with thecomponent. Adhesion between the component and the third material mayalso then take place.

[0031] Additionally the component may have one or more hole, preferablya pattern of a plurality of holes, therein, which are in communicationwith an aperture when the article is in the second mould, so that thethird material can flow via the aperture and into and optionally throughthe hole to thereby form a part of the third material exposed on theouter surface of the article adjacent to the hole on the outer surfaceof the component. In the second mould there may be a cavity adjacentsuch hole so that this exposed third material forms a convex bulge onthe surface of the component.

[0032] The so-formed articles may be removed from respectively the firstor the second mould cavity by conventional means, e.g. conventionalejector pins etc., and may thereafter be handled in further processingoperations by suitable machinery, for example automatic handlingmachinery. Otherwise the first and second moulds may be generallyconventional.

[0033] The invention also provides a moulded article, particularly atoothbrush, being obtainable by such a process.

[0034] Such an article may comprise for example a toothbrush madegenerally of a hard plastics first material, having at least part of itsouter surface provided by a component being a thin sheet or shell of amaterial affixed to the plastics material. This sheet or shell may forexample comprise part of the outer surface of the toothbrush griphandle, for example a decorative and/or reinforcing, and/or gripenhancing thin metal sheet or shell. Such a sheet or shell may forexample be comprised of the materials discussed above, and the sheet orshell may be fixed to the plastics material in the ways described, e.g.by adhesion or anchoring. Such a toothbrush may also have a part,especially a grip pad, made of a third material being a rubbery materialsuch as a thermoplastic elastomer. A part of this third material mayadvantageously pass through the shell from behind the shell and beexposed upon the outer surface of the shell, particularly as a convexbulge, a plurality of which may be arranged in a regular pattern of gripenhancing bulges. Such bulge may for example be generally hemisphericalor generally conical, of diameter ca. 0.75-2.0 mm and projecting ca.0.3-1.0 mm above the outer surface of the shell. Typically such apattern of bulges may be arranged in a regular pattern with theircentres ca. 0.3-1.0 cm, typically ca. 0.4-0.5 cm apart for optimal grip.

[0035] The invention provides an injection mould suitable for such aprocess as described above and suitable for making such a product asdescribed above, particularly a toothbrush.

[0036] The invention will now be described by way of example only withreference to the following Figures.

[0037]FIG. 1 shows two longitudinal sectional views through a two-partinjection mould for a toothbrush

[0038]FIG. 2 shows two cross sections through the mould of FIG. 1 at thepoint A-A

[0039]FIG. 3 shows a longitudinal section through the product made inthe mould of FIGS. 1 and 2

[0040]FIG. 4 shows a sectional view through the product as formed inFIGS. 1 and 2, enclosed in a second injection mould.

[0041]FIG. 5 shows a longitudinal section through a completed toothbrushas formed in the mould of FIG. 4.

[0042] Referring to FIGS. 1 and 2, an injection mould 11 overallcomprises two mould parts 11A, 11B, each of which define between thempart of a mould cavity 12. The two parts 11A, 11B part along split line13. The cavity 12 defines the shape of the skeleton of a toothbrushhaving a grip handle to be formed in part 14 of cavity 12 and a head tobe formed in part 15 of cavity 12, with an intermediate neck region tobe formed in part 16 of cavity 12. The head is formed with holes intowhich bristles may be inserted, by means of pins extending into the part15 of cavity 12 but for simplicity these are not shown.

[0043] Into the cavity 12 has been introduced a component 17, which ispositioned adjacent to and in contact with the inner surface 18 of thecavity 12. The component 17 is a thin shell, made of a decorative metalfoil. Over a large part of its extent the shape of the outer surface ofthe component 17 is convex and corresponds closely to the shape of theinner surface of the cavity 18. Although it is thin, the shell 17 isrigid enough for manipulation and to resist the forces resulting frominjection of the plastic material.

[0044] A vacuum conduit 19 passes through the part 1 1A of the mould.Through the conduit 19 reduced atmospheric pressure may be applied tothe component 17 to hold it in place against the surface 18. In FIG. 1Athe vacuum conduit 19 terminates in a single opening 113 into the cavity12, but in FIG. 1B the vacuum conduit 19 is subdivided into a largenumber of smaller conduits 114 which each terminate in small pinholeopenings into the cavity 12.

[0045] Vacuum may be applied by an external pump and vacuum manifoldsystem of conventional type (not shown).

[0046] The component 17 has holes 110 passing completely through it.Part 11B is formed with internal cores 111 which pass through theseholes 110 and contact surface 18 of part 11A of the mould.

[0047] A melted first fluid plastics material (not shown) is injectedvia gate 112 into the cavity 12, and flows through cavity 12 to form thetoothbrush handle in part 14, the head in part 15, the neck in part 16,and grip handle 14 of the toothbrush. The plastics material also flowsto contact the shell component 17. Adhesion occurs between the shell 17and the plastics material. Additionally or alternatively there may befurther holes in the thin shell material 17, so that the plasticsmaterial can flow into such holes, and optionally through such holes, tothereby engage with the shell 17.

[0048] The outer surface of the shell 17, in contact with the cavitysurface 18, forms the outer surface of the article formed in the cavity12 in the injection process. The assembly of plastic and foil 17 isremoved from the mould using conventional ejector pins (not shown) oncethe plastic material has cooled and hardened.

[0049]FIG. 2B shows a shell 17 provided with anchors or barbs 122 at itsedges which become embedded in the first plastic material and anchor thehardened plastics material and component 17 together. Anchors or barbs(not shown) may be provided at other parts of the shell 17.

[0050]FIG. 3 shows the longitudinal section through the product 31(overall) of this first injection step described above using mould 11.It is seen that the shell 17 is fixed onto the grip handle part 14 byadhesion between shell 17 and the hard plastic material part of theproduct 31, and together the foil 17 and grip handle part 14 form asmooth continuous surface.

[0051] As shown in FIG. 1 the mould cavity in the part 11B is so shapedas to include a convexity 115 which forms a corresponding resultinghollow 116 in the grip handle part of the product 31. Around the cores111 resulting apertures 117 through the hard plastic material part ofproduct 31 have been left when the cores 111 are removed on separationof the parts 11A and 11B of the mould 11.

[0052] In this manner a one-material, i.e. hard plastic material only,toothbrush may be made, with the shell 17 exposed on its outer surface,and for such a purpose the holes 110, cores 111, apertures 117,convexity 115 and hollow 116 are unnecessary and may be absent.

[0053] Referring to FIGS. 4-5 a process for making a two-material, e.g.hard plastic material and elastomeric, i.e. rubbery material, toothbrush51 is illustrated. Using known techniques of toothbrush manufacture theproduct 31 shown in FIG. 3 is introduced into a second injection mould41, again in two half moulds 41A, 41B, with an injection port 42 forinjection of a fluid rubbery material as shown in FIG. 4. The mould 41parts at part line 43. Cavities 44 are provided in mould part 41A incommunication with the holes 110 and apertures 117. The mould part 41Bincludes a cavity 118 in communication with apertures 117 and incommunication with the hollow 116 in the product 31 when this is presentin the mould 41.

[0054] In FIG. 5 the product 51 (overall) obtained by injecting fluidrubbery third material 119 into cavity 118 via port 42 is shown. Therubbery material 119 has thereby formed an elastomer grip pad on thehandle of the product 51. The injected rubbery material 119 has alsoflowed through apertures 117 and holes 110 in the foil 17 to be exposedon the outer surface of the shell 17 to thereby provide decorative andor grip-enhancing features 120 of rubbery material. As shown in FIG. 5the exposed third material bulges convexly from the surface of the shell17, in shapes corresponding to cavities 44, as small grip enhancingbuttons.

[0055] Each bulge 120 is generally hemispherical or generally conical,of diameter ca. 0.75-2.0 mm and projecting ca. 0.3-1.0 mm above theouter surface of the shell. Typically such a pattern of bulges may bearranged in a regular pattern with their centres ca. 0.3-1.0 cm,typically ca. 0.4-0.5 cm apart for optimal grip.

[0056] In the process of the invention the component 17 may bemanipulated and introduced into the mould part 11A by automatedtechniques and conventional robotic technology. The automated operationof injection moulding machines is well known in the head of toothbrushesmade of plastics and rubbery materials. Typically an injection mouldingmachine will include more than one such cavity as 12 and 118. Intoothbrush injection moulding, injection moulding machines with up to 20such cavities fed by a corresponding number of gates such as 112 and 42or a manifold system are commonplace. The process of the invention isapplicable to multiple cavity toothbrush injection moulding machines.

[0057] Although shown as two-part (11A, 11B and 41A, 41B) injectionmoulds, it will be seen that the head 121 of the toothbrush formed inpart 15 of cavity 11 and the part of the toothbrush between the head 121and the handle 14 (i.e. the “neck” region) formed in part 16 of cavity11 are not involved in the second moulding stage in which the rubberymaterial 119 is injected in. Consequently the part of the mould 11 whichencloses the head 121 and neck may be separated from the part of themould 11 which encloses the handle 14 and a further split line (notshown) so that the part of the mould 11 which encloses the head 121 andneck may be used as part of the mould 41.

1. A process for making a moulded article (31) consisting partly of ahard first plastics material characterised by: providing a firstinjection mould (11) having a cavity (12) which defines at least part ofthe shape of the article (31) to be formed and having a cavity surfacebounding the cavity (12); introducing a component (17) into the cavity(12) adjacent to the cavity surface; injecting a first fluid plasticsmaterial into the first mould cavity (12), under conditions such thatthe plastics material flows into contact with the component (17) andwhen the plastics material solidifies the hardened plastic material isfixed to the component (17) and the component (17) forms at least partof the outer surface of the article (31).
 2. A process according toclaim 1 characterised in that the moulded article (31) formed in theprocess is a part or whole toothbrush comprising a grip handle part anda head part (121) into which bristles may be fixed.
 3. A processaccording to claim 1 or 2 characterised in that the component (17) ismade of thin sheet form metal, plastic or a metal-plastic laminate orcomposite.
 4. A process according to claim 3 characterised in that thecomponent (17) comprises a thin shell, a surface of which forms at leastpart of the outer surface of a finished toothbrush (51).
 5. A processaccording to any one of the preceding claims characterised in that thecomponent (17) is held in place in the cavity (12) in contact with thecavity surface by the application of reduced atmospheric pressure to thecomponent via a conduit (19) in the mould and opening into the firstmould cavity (12), sucking the component (17) against the cavitysurface.
 6. A process according to any one of the preceding claimscharacterised in that the so-formed article (31) comprising the firstmaterial and the component (17) is further processed in a secondmoulding operation by: providing a second injection mould part (41)having a second mould cavity (118) therein; introducing the so-formedarticle (31) into the second mould cavity (118) of the second injectionmould part (41); injecting a melted fluid third material (119) into thesecond mould cavity (118) and into contact with the so-formed article(31); allowing the melted fluid third material to solidify sufficientlyand such that when the third material solidifies the hardened thirdmaterial is fixed to the article (51).
 7. A process according to claim 6characterised in that the third material (119) is a rubbery material. 8.A process according to claim 6 or 7 characterised in that one or morehollow (116) is provided in the article (31) formed in the firstmoulding operation, suitable to receive, and be wholly or partiallyfilled with, the third material (118) in the second moulding step.
 9. Aprocess according to any one of claims 6, 7 or 8 characterised in thatthe article (31) formed in the first injection moulding stage is formedwith one or more aperture (117) in its structure so that the thirdmaterial (119) may flow through the aperture (117) and flow to parts ofthe article (31) distanced from the injection gate of the third material(118).
 10. A process according to claim 9 characterised in that thecomponent (17) has one or more hole (110) therein, in communication withan aperture (117) when the article is in the second mould (41), so thatthe third material (119) can flow via the aperture (117) and into andoptionally through the hole (110) to thereby form a part (120) of thethird material exposed on the outer surface of the component (17).
 11. Aprocess according to claim 10 characterised in that in the second mould(41) there is a cavity (44) adjacent a hole (110) so that the exposedthird material forms a convex bulge (120) on the surface of thecomponent (17).
 12. A moulded toothbrush (51), being obtainable by aprocess as claimed in any one of claims 1 to
 11. 13. A toothbrush (51)according to claim 12 made generally of a hard plastics first materialhaving at least part of its surface provided by a component (17) being athin sheet or shell of a material affixed to the plastics material whichcomprises part of the outer surface of the toothbrush grip handle.
 14. Atoothbrush (51) characterised by being made generally of a first hardplastics first material having at least part of its surface provided bya component being a thin shell (17) of a second material affixed to thehard plastics material, the shell (17) comprising part of the outersurface of the toothbrush (51) grip handle, the toothbrush having a grippad (119) made a third material being a rubbery material, a part of thethird material passing through the shell (17) from behind the shell (17)and being exposed upon the outer surface of the shell (17) as a convexbulge (120).
 15. An injection mould (11, 41) suitable for a process asclaimed in any one of claims 1 to 11.